Doh! I thought you were talking about built up wings I should have searched your for the model your building.
when most people refer to "glassing "they are talking about epoxy as the resin over a light grade of fiberglass usually around .75oz in weight it looks alot like silk fabric and adds strength as well as a base for painting.

a popular product is called Z-poxy its a thinner version than the stuff used in general building and construction,after joining the wing halfs you could also beef up the joint by using a slightly heavyer glass for strength in a 2-4" wide strip around the center of the wing.

again even when using epoxy for strenthening the joint more adhesive doesn't make the joint stronger,its the fiberglass that adds the strength,when you "wet" the fiberglass squeege the exess epoxy from the cloth so the cloth is tight to the surface you can always add more adhesive later if you feel theres not enough,as long as the cloth is saturated,and has the wet look, you should be fine and will have a strong center section when its dry.

I would think the sig glue is a foam specific adhesive so for the initial joining use the recomended adhesive, the glass at the center section is more of a insurance policy against failure.